Messages in this thread | | | Date | Thu, 26 Jan 2006 12:42:09 +0530 | From | Balbir Singh <> | Subject | Re: [PATCH 8/12] generic hweight{32,16,8}() |
| |
On 1/26/06, Akinobu Mita <mita@miraclelinux.com> wrote: > This patch introduces the C-language equivalents of the functions below: > unsigned int hweight32(unsigned int w); > unsigned int hweight16(unsigned int w); > unsigned int hweight8(unsigned int w); > > HAVE_ARCH_HWEIGHT_BITOPS is defined when the architecture has its own > version of these functions. > > This code largely copied from: > include/linux/bitops.h > > Index: 2.6-git/include/asm-generic/bitops.h > =================================================================== > --- 2.6-git.orig/include/asm-generic/bitops.h 2006-01-25 19:14:10.000000000 +0900 > +++ 2.6-git/include/asm-generic/bitops.h 2006-01-25 19:14:11.000000000 +0900 > @@ -458,14 +458,38 @@ > #endif /* HAVE_ARCH_FFS_BITOPS */ > > > +#ifndef HAVE_ARCH_HWEIGHT_BITOPS > + > /* > * hweightN: returns the hamming weight (i.e. the number > * of bits set) of a N-bit word > */ > > -#define hweight32(x) generic_hweight32(x) > -#define hweight16(x) generic_hweight16(x) > -#define hweight8(x) generic_hweight8(x) > +static inline unsigned int hweight32(unsigned int w) > +{ > + unsigned int res = (w & 0x55555555) + ((w >> 1) & 0x55555555); > + res = (res & 0x33333333) + ((res >> 2) & 0x33333333); > + res = (res & 0x0F0F0F0F) + ((res >> 4) & 0x0F0F0F0F); > + res = (res & 0x00FF00FF) + ((res >> 8) & 0x00FF00FF); > + return (res & 0x0000FFFF) + ((res >> 16) & 0x0000FFFF); > +} > +
This can be replaced with
register int res=w; res=res-((res>>1)&0x55555555); res=(res&0x33333333)+((res>>2)&0x33333333); res=(res+(res>>4))&0x0f0f0f0f; res=res+(res>>8); return (res+(res>>16)) & 0xff;
Similar optimizations can be applied to the routines below. Please see http://www-cs-faculty.stanford.edu/~knuth/mmixware.html errata and the code in mmix-arith.w for the complete set of optimizations and credits.
http://www.jjj.de/fxt/fxtbook.pdf is another inspirational source for such algorithms.
> +static inline unsigned int hweight16(unsigned int w) > +{ > + unsigned int res = (w & 0x5555) + ((w >> 1) & 0x5555); > + res = (res & 0x3333) + ((res >> 2) & 0x3333); > + res = (res & 0x0F0F) + ((res >> 4) & 0x0F0F); > + return (res & 0x00FF) + ((res >> 8) & 0x00FF); > +} > + > +static inline unsigned int hweight8(unsigned int w) > +{ > + unsigned int res = (w & 0x55) + ((w >> 1) & 0x55); > + res = (res & 0x33) + ((res >> 2) & 0x33); > + return (res & 0x0F) + ((res >> 4) & 0x0F); > +} > + > +#endif /* HAVE_ARCH_HWEIGHT_BITOPS */ > > #endif /* __KERNEL__ */
Regards, Balbir - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |